Page - 209 - in Proceedings - OAGM & ARW Joint Workshop 2016 on "Computer Vision and Robotics“

Design,ModelingandControlofanExperimental RedundantlyActuatedParallelPlatform∗ KyrillKrajoski1,AndreasMu¨ller1,HubertGattringer1 andMatthias Jo¨rgl1,2 1 InstituteofRobotics JohannesKeplerUniversityLinz,Austria {kyrill.krajoski, a.mueller, hubert.gattringer,matthias.joergl}@jku.at 2 TrotecGmbH,Austria Abstract Actuationredundancyisameanstoimprovethedexterity,accuracyandreliabilityofparallelmanipu- lators(PKMs).Over thelastdecade,variousnoveldesignsandcontrolconceptshavebeendeveloped and implemented in functionalprototypes. In spite thisextensiveresearchseveral fundamental issues still remain to be addressed. This requires test benches allowing for flexible andmodular setup of PKMprototypes. Aimingat agile light-weightPKMs, sucha test bed should in particular enable to replacerigidbyelastic links,and to implementmodel-basedrobustcontrol concepts. Such an experimental test platform is presented in this paper. The PKM under investigation is a 2-DOFplanarPKMredundantly actuated by three actuators. Itsmechanical design and actuation concepts togetherwith the control systemare presented. Thedynamicalmodel is presentedas basis for thenon-linearcontrol. Fullyparallelmanipulatorsarecharacterizedbyrepetitiveuseof identical modules connecting themoving and fixed platform. Therefore emphasize is given to the submodel- ing concept, which allows seamless integrationof differentmodules (rigid vs. flexible links). Initial resultsare reported for the2-PKMwhencontrolledbyanaugmentedPDscheme. 1. Introduction Themainpurposeof thepresentedresearch is tocreateamodularparallelmanipulatorwithactuation redundancyas a test platform. Thedynamicsmodeling is carriedoutbymeansof subsystemmodel- ing, see [1], [3] for details. The key for flexible and quickmanufacturing is rapid prototyping. The prototypehas linkswith lowmassand inertiaandare3Dprinted. Themodularity allows for two, three, or four arms, connecting themovingplatform, and thus gives rise to actuation redundancy. Amodel-based control scheme is used. This is based on a non-linear dynamicmodel. In this paper a computationallyefficient formulation is used in termsofminimal as well as redundant coordinates [2], [4], [8], [7]. These dynamicmodels are the basis for the inverse dynamics and later for the augmented PD controller. Because of actuation redundancy, the inverse dynamic can be extended by a null space term, wich does not affect themanipulator’smotion. It admits to increase thepreload toannihilatebacklashormanipulate theendeffector (EE) stiffness [9], [5], [6]. Finally, simulationresultsof anaugmentedPDcontroller arepresentedandanalyzed. ∗Thisworkhasbeensupportedby theAustrianCOMET-K2programof theLinzCenterofMechatronics(LCM),and was fundedby theAustrian federalgovernmentand the federal stateofUpperAustria. 209